There are not enough rocket scientist cancer people out there who could deny this one but it took a study about parents of children with cancer and a referral to a study of stress on breast cancer patients to paint the big picture. A cancer diagnosis is stressful - well DOH! - whether its you or a family member.
I think the issue of the stress level of family members is finally getting more attention. A cancer diagnosis does a number on everyone in the family. I have seen more emotional people talking about their family member's cancer and fewer emotions from the patients themselves. A cancer diagnosis is hard to cope with - facing the unknown.
If you are the patient in treatment, you get a whole group of people to help you - doctor, nurses, social workers, etc - who are on call 24/7 for everything from the sniffles to new symptoms. You get lots of TLC. They want to make sure you stay healthy enough to continue your treatment and are not reacting to it in bad ways.
If you are a family member of a cancer patient, its close but not the same. The doctors are focusing on the patient but include you in the conversation. You may be able to see more of the big picture but that doesn't mean it is a rosy, optimistic one.
I have been on both sides of this lovely little situation so I can tell you its not easy either side. At my first cancer diagnosis, I was a kid, I didn't really cope. At my second diagnosis, I was much more proactive and said 'look, tell me the information'. Then with my husband's diagnosis, I spoke up and said to the surgeon 'I've had cancer twice so we have an idea of what to expect for treatment options'. That actually was a good idea as the surgeon opened up and talked to us more.
It should not be a surprise that the word cancer has nasty overtones (hurry up with the damn cure will you?). And the resulting level of stress can do nasty things to your sanity, brain, and body. I think talking about it as opposed to ignoring the giant elephant in the room will make a huge difference. But the stress will take a long time to go away, if ever.